Reflection element of exposure light and production method therefor, mask, exposure system, and production method of semiconductor device

ABSTRACT

A reflector for extreme ultraviolet light, its manufacture method, a phase shift mask, an exposure apparatus and a semiconductor manufacture method, capable of making the wavelength dependency of a reflectance via a plurality of reflection surfaces be coincident with an center wavelength of exposure light of exposure light and retaining a sufficient energy reaching a subject to be exposed. The reflector for exposure light to be used for exposure of a subject to be exposed in a lithography process of manufacturing a semiconductor device is configured to have a multi-layer film structure made by repetitively stacking a plurality of layers in the same order. The periodical length of the repetitive stack unit of the multi-layer film structure is set in such a manner that the center of full width at half maximum of the reflectance via a predetermined number of reflectors becomes coincident with the center wavelength of extreme ultraviolet light to be reflected (S 102 ).

TECHNICAL FIELD

The present invention relates to a reflector for exposure light having afunction of reflecting exposure light, such as mask blanks of exposuremasks and reflection mirrors, the reflector being used when a circuitpattern is transferred by exposure light to a subject to be exposed suchas a wafer in a lithograph process of manufacturing a semiconductordevice, and to a reflector manufacture method. The present inventionalso relates to a mask having a function of reflecting exposure light.The present invention also relates to an exposure apparatus constitutedof exposure light reflectors. The present invention also relates to asemiconductor device manufacture method using an exposure light mask.

BACKGROUND ART

Recent fine semiconductor devices require to minimize a pattern width(line width), a pitch between patterns and the like of a circuit patternto be formed on a wafer and or a resist pattern for forming the circuitpattern and the like. This minimization request can be dealt with byshortening the wavelength of ultraviolet light to be used as exposurelight to resist. As miniaturization of semiconductor devices progressesmore, the wavelength of ultraviolet light to be used as exposure lightis shortened to, for example, a wavelength of 365 nm for semiconductordevices under a 350 nm design rule, a wavelength of 248 nm forsemiconductor devices under a 250 nm and 180 nm design rule, and awavelength of 193 nm for semiconductor devices under a 130 nm and 100 nmdesign rule, ultraviolet light having a wavelength of 157 nm being nowin use.

It is know that a resolution relative to a wavelength is generallyexpressed by the Rayleigh's equation w=k1×(λ/NA) where w is a minimumwidth pattern to be resolved, NA is a numerical aperture of a lens in aprojection optical system, λ is a wavelength of exposure light and k1 isa process constant. The process constant is determined mainly by theperformance of resist, selection of ultra resolution techniques and thelike. It is known that k1 can be selected to be about 0.35 if optimumresist and ultra resolution techniques are used. According to the ultraresolution techniques, ±first order refraction light of lighttransmitted through a mask and refracted by a mask light shieldingpattern is selectively used to obtain a pattern smaller than thewavelength.

It can be known from the Rayleigh's equation that the minimum patternwidth capable of being dealt with if a wavelength of, for example, 157nm is used, is w=61 nm by using a lens with NA=0.9. Namely, if a patternwidth narrower than 61 nm is to be obtained, it is necessary to useultraviolet light having a wavelength shorter than 157 nm.

From this reason, studies have been made recently to use light having awavelength of 13.5 nm called extreme ultraviolet (EUV; Extreme UltraViolet) light as ultraviolet light having a wavelength shorter than 157nm. Since there is light transmission material such as CaF₂ (calciumfluoride) and SiO₂ (silicon dioxide) for ultraviolet light having awavelength of 157 nm or longer, it is possible to form a mask and anoptical system capable of transmitting the ultraviolet light. However,for the extreme ultraviolet light having a wavelength of 13.5 nm,material capable of transmitting the extreme ultraviolet light at adesired thickness does not exist. Therefore, if the extreme ultravioletlight having a wavelength of 13.5 nm is used, not a mask and an opticalsystem of a light transmission type, but a mask and an optical system ofa light reflection type is required to be used.

If a mask and an optical system of the light reflection type are used,light reflected from a mask surface is required to be guided to aprojection optical system without being interfered with light incidentupon the mask. It is therefore essential that light incident upon themask is required to be oblique at an angle φ relative to the normal tothe mask surface. This angle is determined from the numerical apertureNA of a lens in a projection optical system, a mask multiplication m anda size σ of an illumination light source. Specifically, in an exposureapparatus with NA=0.3 and σ=0.8, light is incident upon a mask, having asolid angle of 3.44±2.75 degrees. If a mask having a reduction factor of4 relative to a wafer is used and an exposure apparatus has NA=0.25 andσ=0.7, light is incident upon the mask, having a solid angle of3.58±2.51 degrees.

As a reflection type mask for use with oblique incidence light, a maskblank is known which reflects extreme ultraviolet light and has anabsorption film covering the mask blank with a predetermined pattern andabsorbing extreme ultraviolet light and a buffer film interposed betweenthe mask blank and absorption film. The mask blank has the structurethat an Si (silicon) layer and an Mo (molybdenum) layer are alternatelystacked, and the repetition number of stacks is generally 40 layers.Since the absorption film for extreme ultraviolet light covers the maskblank with a predetermined pattern, incidence light is selectivelyreflected in accordance with a circuit pattern to be formed, a resistpattern or the like. The buffer film is formed, as an etching stopperwhen the absorption film is formed, or in order to avoid damages to becaused when defects are removed after the absorption mask is formed.

As described above, a conventional mask blank has generally 40 layers asthe repetition number of stacks of the Si layer and Mo layer. Areflectance of Si is 0.9993-0.00182645i and a reflectance of Mo is0.9211-0.00643543i, where i is an imaginary unit. It is known that aproper ratio r of a Mo layer thickness to a total thickness of the Silayer and Mo layer is Mo layer thickness/(Si layer thickness+Mo layerthickness)=0.4. Therefore, in a conventional mask blank, if thewavelength λ of extreme ultraviolet light to be used for exposure is13.5 nm, the total thickness of the Si layer and Mo layer is(λ/2)/(0.9993×0.6+0.9211×0.4)=6.973 nm, a thickness of the Si layer is6.9730×0.6=4.184, and a thickness of an Mo layer is 6.9730×0.4=2.789 nm.FIG. 1 shows a reflectance of the mask blank having 40 layers of thestack of the Si layer and Mo layer described above. In the example shownin FIG. 1, the reflectance is at an incidence angle of 4.84 degrees. Theincidence angle is defined as an angle relative to the normal to thesurface of the mask blank.

The structure that the Si layer and Mo layer are alternately stacked isused not only for a mask blank of the reflection type but also for areflection mirror constituting a reflection type optical system in quitea similar manner. Namely, the reflection mirror for extreme ultravioletlight has generally 40 layers as the repetition number of stacks of theSi layer and Mo layer, and the reflectance shown in FIG. 1 is obtainedby properly setting the thicknesses of the Si layer and Mo layer whenthe wavelength of extreme ultraviolet light is 13.5 nm.

Extreme ultraviolet light generally propagates via a plurality ofreflection surfaces from a light source of an exposure apparatus toresist coated on a wafer, for example, six mirror reflection surfaces ofan illumination optical system, six mirror reflection surfaces of aprojection optical system and one reflection surface of a mask, thirteensurfaces in total. Extreme ultraviolet light emitted from the lightsource is attenuated upon reflection at a reflection surface. If thisattenuation is large, sufficient energy cannot reach the resist coatedon the wafer and there is a fear that pattern formation and the likecannot be performed properly.

If extreme ultraviolet light propagates via a plurality of reflectionsurfaces, the energy reaching the resist coated on a wafer can beestimated from a reflectance at each of the plurality of reflectionsurfaces and a light source intensity. A reflectance R via a pluralityof reflection planes is given by the following equation (1) if the lightpropagates via thirteen reflection surfaces in total. R_(TE) is areflectance of a TE wave per one reflection surface and R_(TM) is areflectance of a TM wave per one reflection surface.R={(R _(TE) +R _(TM))/2}¹³  (1)

A reflectance R of thirteen surfaces in total was obtained by using theequation (1) when the mask blank and reflection mirrors having thereflectance shown in FIG. 1 are used. The reflectance R is as shown inFIG. 4. It can be seen from the example shown in FIG. 4 that the centerof the half width of a spectrum of the reflectance R is not coincidentwith 13.5 nm which is the center wavelength of exposure light of extremeultraviolet light. Namely, even if the center of FWHM (Full Width atHalf Maximum) of a reflectance per one reflection surface is coincidentwith the center wavelength of exposure light (refer to FIG. 1), thecenter of FWHM of the reflectance R via thirteen reflection surfaces intotal is not necessarily coincident with the center wavelength ofexposure light and the wavelength dependency may deviate from the centerwavelength of exposure light. This results from that the peak wavelengthfor the reflectance per one reflection surface is not coincident with13.5 nm which is the center wavelength of exposure light of extremeultraviolet light. As above, if the wavelength dependency of thereflectance via a plurality of reflection surfaces deviates from thecenter wavelength of exposure light of extreme ultraviolet light,attenuation at the center wavelength of exposure light, i.e.,attenuation of a light source intensity of the light source, becomeslarge. Therefore, sufficient energy will not reach at an exposure lightwavelength suitable for resist coated on a wafer, and the probabilitythat pattern formation and the like cannot be performed properly becomesvery high.

It is therefore an object of the present invention to provide areflector for exposure light which can retain a sufficient energyreaching a subject to be exposed, by making the wavelength dependency ofa reflectance via a plurality of reflection surfaces be coincident withthe center wavelength of exposure light of exposure light such asextreme ultraviolet light.

In a lithography process for manufacturing a semiconductor device, anumber (a variety) of exposure masks is used in some cases. Further, ifthere are a plurality of exposure apparatuses and manufacture isexecuted at a plurality of factories, a plurality of exposure masks areoften used even for the same product and even in the same process. Insuch cases, it is fairly conceivable that thicknesses of films and thelike constituting each of a plurality of exposure masks have amanufacture variation.

The manufacture variation of this type, i.e., a thickness variation offilms and the like constituting each exposure mask, causes a deviationof the center of FWHM of the reflectance relative to extreme ultravioletlight, which may result in a reduction in arrival energy at an exposurelight wavelength suitable for resist coated on a wafer. It is thereforedesired to remove the variation as much as possible. However, forexample, when the productivity of mask blanks is considered, it is notrealistic to limit the film thickness and the like too severely.

It is therefore an object of the present invention to provide areflector for exposure light, its manufacture method, a mask, anexposure apparatus and a semiconductor device manufacture method, whichcan retain a sufficient energy reaching a subject to be exposed, bymaking the wavelength dependency of a reflectance via a plurality ofreflection surfaces be coincident with the center wavelength of exposurelight of exposure light such as extreme ultraviolet light.

DISCLOSURE OF THE INVENTION

The present invention is a reflector for exposure light devised in orderto achieve the above-described objects. The reflector for exposure lightis characterized in that it has a multi-layer film structure that aplurality of layers are repetitively stacked in the same order, that aperiodical length of a repetitive stack unit of the multi-layer filmstructure is set so that a center of FWHM of a reflectance via apredetermined number of reflectors becomes coincident with a centerwavelength of exposure light to be reflected, and that the reflector isused when the exposure light is exposed to a subject to be exposed in alithography process for manufacture of a semiconductor device.

In addition to the periodical length of the repetitive stack unit of themulti-layer film structure, a film thickness ratio between a pluralityof layers constituting the repetitive stack unit may also be set so thatthe center of FWHM of the reflectance via the predetermined number ofreflectors becomes coincident with the center wavelength of exposurelight to be reflected.

The present invention is a method of manufacturing a reflector forexposure light devised in order to achieve the above-described object.Namely, the method is characterized in that a multi-layer film structuremade by repetitively stacking a plurality of layers in the same order isformed by setting a periodical length of a repetitive stack unit of themulti-layer film structure and a film thickness ratio between aplurality of layers constituting the repetitive stack unit in such amanner that a center of FWHM of a reflectance via a predetermined numberof reflectors becomes coincident with a center wavelength of exposurelight to be reflected.

The present invention is a mask devised in order to achieve theabove-described object and used when exposure light is exposed to asubject to be exposed in a lithography process for manufacture of asemiconductor device. The mask is characterized by including a reflectorportion having a multi-layer film structure made by repetitivelystacking a plurality of layers in the same order and an absorption filmportion covering the reflector portion with a predetermined pattern,wherein the mask is structured so that there is a phase differencebetween reflection light of exposure light from the reflector portionand reflection light of the exposure light from the absorption filmportion, and that in the reflection portion a periodical length of arepetitive stack unit of the multi-layer film structure and a filmthickness ratio between the plurality of layers constituting therepetitive stack unit are set so that a center of FWHM of a reflectancevia a predetermined number of reflectors becomes coincident with acenter wavelength of exposure light to be reflected.

The present invention is an exposure apparatus devised in order toachieve the above-described object and used when exposure light isexposed to a subject to be exposed in a lithography process formanufacture of a semiconductor device. The exposure apparatus ischaracterized by including a predetermined number of reflectors forexposure light, the reflector having a multi-layer film structure madeby repetitively stacking a plurality of layers in the same order,wherein in the reflector for exposure light a periodical length of arepetitive stack unit of the multi-layer film structure and a filmthickness ratio between the plurality of layers constituting therepetitive stack unit are set so that a center of FWHM of a reflectancevia the predetermined number of reflectors becomes coincident with acenter wavelength of exposure light to be reflected.

The present invention is a semiconductor device manufacture methoddevised in order to achieve the above-described object. Thesemiconductor device manufacture method is characterized by including areflector portion having a multi-layer film structure made byrepetitively stacking a plurality of layers in the same order and anabsorption film portion covering the reflector portion with apredetermined pattern, wherein exposure light is exposed to a subject tobe exposed in a lithography process for manufacture of a semiconductordevice, by using a mask structured so that there is a phase differencebetween reflection light of exposure light from the reflector portionand reflection light of the exposure light from the absorption filmportion, and that in the reflection portion a periodical length of arepetitive stack unit of the multi-layer film structure and a filmthickness ratio of the plurality of layers constituting the repetitivestack unit are set so that a center of FWHM of a reflectance via apredetermined number of reflectors becomes coincident with a centerwavelength of exposure light to be reflected.

According to the above-described reflector for exposure light, theperiodical length of the repetitive stack unit of the multi-layer filmstructure is set so that the center of FWHM of the reflectance via apredetermined number of reflectors becomes coincident with the centerwavelength of exposure light to be reflected. Therefore, the reflectanceof exposure light via the predetermined number of reflectors iscoincident with the center wavelength of the exposure light.Accordingly, attenuation of the exposure light intensity can beprevented from becoming large even if the exposure light propagates viathe predetermined number of reflectors, and it is possible to retainsufficient arrival energy when exposure to the subject to be exposed isexecuted.

Further, according to the above-described reflector for exposure light,its manufacture method, mask, exposure apparatus and semiconductordevice manufacture method, the periodical length of the repetitive stackunit of the multi-layer film structure and the film thickness ratioamong a plurality of layers constituting the repetitive stack unit areset so that the center of FWHM of the reflectance via a predeterminednumber of reflectors becomes coincident with the center wavelength ofexposure light to be reflected. Namely, by setting also the filmthickness ratio between a plurality of layers, the center of FWHM of thereflectance becomes coincident with the center wavelength of exposurelight even if the total film thickness of the multi-layer film structureis shifted. Accordingly, an allowable variation width of the total filmthickness of the multi-layer film structure can be broadened. Even inthis case, attenuation of the exposure light intensity can be preventedfrom becoming large, and it is possible to retain sufficient arrivalenergy when exposure to the subject to be exposed is executed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustrative diagram showing an example of reflectanceswhen a single reflector is used for extreme ultraviolet light, and morespecifically a diagram showing reflectances by one reflector surface ofa multi-layer film structure made by stacking 40 layers of Si 4.184nm/Mo 2.789 nm at a periodical length 6.973 nm of a film thickness.

FIG. 2 is a cross sectional side view showing an example of the outlinestructure of a reflector for exposure light according to the presentinvention.

FIG. 3 is a perspective view showing an example of the outline structureof a mask according to the present invention.

FIG. 4 is an illustrative diagram showing an example of reflectanceswhen extreme ultraviolet light propagates via a plurality of reflectors,and more specifically a diagram showing reflectances by thirteenreflector surfaces each constituted of a multi-layer film structure madeby stacking 40 layers of Si 4.184 nm/Mo 2.789 nm at a periodical length6.973 nm of a film thickness.

FIG. 5 is an illustrative diagram showing an example of reflectanceswhen extreme ultraviolet light propagates via a single reflectoraccording to the present invention, and more specifically a diagramshowing reflectances by a single reflector surface constituted of amulti-layer film structure made by stacking 40 layers of Si 4.17 nm/Mo2.78 nm at a periodical length 6.95 nm of a film thickness.

FIG. 6 is an illustrative diagram showing an example of reflectanceswhen extreme ultraviolet light propagates via a plurality of reflectorsaccording to the present invention, and more specifically a diagramshowing reflectances by thirteen reflector surfaces each constituted ofa multi-layer film structure made by stacking 40 layers of Si 4.17 nm/Mo2.78 nm at a periodical length 6.95 nm of a film thickness.

FIG. 7 is a flow chart illustrating an example of a manufactureprocedure for a reflector to be used with extreme ultraviolet lightaccording to the present invention.

FIG. 8 is an illustrative diagram showing an example of the results ofrelative energies reaching wafers when there is a film thicknessvariation of respective layers constituting a multi-layer filmstructure.

FIG. 9 is an illustrative diagram showing an example of reflectances bya single reflector when there is a variation of total film thicknessesof multi-layer film structures, and more specifically a diagram showingreflectances R_(mask) of thinner and thicker cases of the total filmthickness d_(total)=278 nm of a multi-layer film structure made bystacking 40 layers of Si 4.17 nm/Mo 2.78 nm at a periodical length 6.95nm of a film thickness.

FIG. 10 is an illustrative diagram showing an example of reflectances bya plurality of reflectors when there is a variation of total filmthicknesses of multi-layer film structures, and more specifically adiagram showing reflectances R_(total) by twelve multi-layer filmmirrors each having a total thickness d_(total)=278 nm and manufacturedby stacking 40 layers of Si 4.17 nm/Mo 2.78 nm at a periodical length6.95 nm of a film thickness and via one mask blank having themulti-layer film structure and a variation of total film thicknessesd_(total).

FIG. 11 is an illustrative diagram showing an example of relativeenergies reaching wafers when there is a variation of total thicknessesof multi-layer film structures, and more specifically a diagram showingrelative energies E_(relative) via the propagation route of twelvemulti-layer film mirrors each having a total thickness d_(total)=278 nmand manufactured by stacking 40 layers of Si 4.17 nm/Mo 2.78 nm at aperiodical length 6.95 nm of a film thickness and one mask blank havingthe multi-layer film structure and a variation of the total filmthicknesses d_(total).

FIG. 12 is an illustrative diagram showing an example of the relationbetween a periodical length of a film thickness and an optimum r valueof a multi-layer film structure.

FIG. 13 is an illustrative diagram showing an example of reflectances bya single reflector for extreme ultraviolet light having an optimum Γvalue according to the present invention, and more specifically adiagram showi reflectances R_(mask) by one reflector surface of amulti-layer film structure having an optimum combination of a total filmthickness d_(total) and a Γ value and made by stacking 40 layers of Si4.17 nm/Mo 2.78 nm at a periodical length 6.95 nm of a film thickness.

FIG. 14 is an illustrative diagram showing an example of reflectances bya plurality of reflectors for extreme ultraviolet light having anoptimum Γ value according to the present invention, and morespecifically a diagram showing reflectances R_(total) by twelvemulti-layer film mirrors each having a total thickness d_(total)=278 nmand manufactured by stacking 40 layers of Si 4.17 nm/Mo 2.78 nm at aperiodical length 6.95 nm of a film thickness and by one mask blankhaving an optimum Γ value.

FIG. 15 is an illustrative diagram showing an example of relativeenergies reaching wafers via a plurality of reflectors for extremeultraviolet light having an optimum Γ value according to the presentinvention, and more specifically a diagram showing relative energiesE_(relative) via the propagation route of twelve multi-layer filmmirrors each having a total thickness d_(total)=278 nm and manufacturedby stacking 40 layers of Si 4.17 nm/Mo 2.78 nm at a periodical length6.95 nm of a film thickness and one mask blank having an optimum Γvalue.

FIG. 16 is an illustrative diagram showing an example of the resultsobtained by plotting allowable variation values of a total filmthickness as a function of a relative energy, for both the cases whereina Γ value is optimized and not optimized.

FIG. 17 is an illustrative diagram showing an example of TE wave phasedifference distributions of a half tone phase shift mask at respectivewavelengths, relative to a variation of total film thicknesses when a Γvalue is not optimized.

FIG. 18 is an illustrative diagram showing an example of TM wave phasedifference distributions of a half tone phase shift mask at respectivewavelengths, relative to a variation of total film thicknesses when a Γvalue is not optimized.

FIG. 19 is an illustrative diagram showing an example of TE wave phasedifference distributions of a half tone phase shift mask at respectivewavelengths, relative to a variation of total film thicknesses when a Γvalue is optimized.

FIG. 20 is an illustrative diagram showing an example of TM wave phasedifference distributions of a half tone phase shift mask at respectivewavelengths, relative to a variation of total film thicknesses when a Γvalue is optimized.

FIG. 21 is an illustrative diagram showing an example of reflectanceratio distributions of a half tone phase shift mask at respectivewavelengths, relative to a variation of total film thicknesses when a Γvalue is not optimized.

FIG. 22 is an illustrative diagram showing an example of reflectanceratio distributions of a half tone phase shift mask at respectivewavelengths, relative to a variation of total film thicknesses when a Γvalue is optimized.

FIG. 23 is a schematic diagram showing an example of the outlinestructure of an exposure apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, description will be made on a reflectorfor extreme ultraviolet light and its manufacture method, a phase shiftmask and an exposure apparatus according to the invention. It is obviousthat the present invention is not limited to preferred embodiments to bedescribed below.

First, an example of an exposure apparatus will be described. Theexposure apparatus described herein is used for exposing a subject(resist on a wafer) to extreme ultraviolet light in a manufactureprocess for semiconductor devices, particularly in a lithography processof transferring a circuit pattern of a semiconductor device from anexposure mask to a wafer. More in detail, the route from a light sourcefor irradiating extreme ultraviolet light having a center wavelength of13.5 nm to resist on a wafer which is a subject to be exposed, isstructured so that extreme ultraviolet light propagates via thirteenreflection surfaces in total, twelve mirror reflection surfaces of anoptical system and one reflection surface of an exposure mask.

Next, description will be made on a reflector for extreme ultravioletlight to be used by this exposure apparatus, i.e., a reflector forextreme ultraviolet light according to the present invention. Thereflector for extreme ultraviolet light described herein is used as areflection mirror constituting a mirror reflection surface of an opticalsystem or a mask blank constituting a reflection surface of an exposuremask. More in detail, as shown in FIG. 2, the reflector has amulti-layer film structure made by repetitively stacking 40 layers eachconstituted of an Si layer 2 and an Mo layer 3 in the same order ofMo/Si/Mo/Si, . . . , Mo/Si from a low expansion glass 1 of, for example,SiO₂ (silicon dioxide) or the like toward the reflector surface (frontsurface). The reflector 4 having the multi-layer film structure of thistype may be formed by ion beam sputtering. More specifically, the Silayer 2 and Mo layer 3 are formed at predetermined film forming speedsby using, for example, an ion beam sputtering system.

In order to configure a reflection type exposure mask by using thereflector 4, as shown in FIG. 3 an absorption film 6 made of extremeultraviolet light absorbing material such as TaN (tantalum nitride) isformed on the reflector 4, with a buffer film 5 made of Ru (ruthenium)or the like being interposed therebetween. Namely, a light reflectionsurface side of the reflector 4 is covered with the absorption film 6having a predetermined pattern so that incidence light can beselectively reflected in correspondence with a circuit pattern, resistpattern or the like to be formed. If a reflection mirror is to beconfigured, the light reflection surface of the reflector is used as itis to reflect incidence light. For example, as the optical conditions, acenter wavelength (exposure wavelength) of extreme ultraviolet light asincidence light is set to 13.5 nm, and as the exposure conditions,NA=0.25 and σ=0.70.

As already described, since the reflector having the multi-layer filmstructure of this type has an Si reflectance of 0.9993-0.00182645i, anMo reflectance of 0.9211-0.00643543i and an extreme ultraviolet lightwavelength λ of 13.5 nm, generally a ratio Γ of a thickness of the Molayer to a total thickness of the Si layer and Mo layer is set to 0.4, atotal thickness of the Si layer and Mo layer is set to(λ/2)/(0.9993×0.6+0.9211×0.4)=6.973 nm, a thickness of the Si layer isset to 6.9730×0.6=4.184 nm and a thickness of the Mo layer is set to6.9730×0.4=2.789 nm. However, with the reflector having the multi-layerfilm structure constructed as above, as shown in FIG. 1, although thecenter of FWHM of the reflectance by a single reflector is coincidentwith the center wavelength of exposure light, the peak wavelength isshifted from the center wavelength of exposure light. Therefore, asshown in FIG. 4, the wavelength dependency of the reflectance R via thepropagation route of thirteen reflection surfaces in total may shiftfrom the center wavelength of exposure light because the center of FWHMis not always coincident with the center wavelength of exposure light.

The reflector 4 having the multi-layer film structure described in thispreferred embodiment is designed to have a periodical length of a filmthickness of a repetitive stack unit of the Si layer 2 and Mo layer 3,different from a conventional design, in order to make the reflectancebecome coincident with the center wavelength of exposure light so thatsufficient energy reaching resist can be retained even if thepropagation route via thirteen reflection surfaces in total is used.Namely, with the reflector 4 described in the preferred embodiment, theperiodical length of the repetitive stack unit of the multi-layer filmstructure is set so that the center of FWHM of the reflectance via thethirteen reflection surfaces in total becomes coincident with the centerwavelength of extreme ultraviolet light.

More specifically, a shift is considered between the peak wavelength ofthe reflectance by a single reflector and the center wavelength ofexposure light. A correction corresponding to this shift amount is addedto the value of the wavelength λ of extreme ultraviolet light and thetotal thickness of the Si layer 2 and Mo layer 3 is identified by anequation of (λ/2)/(0.9997×0.6+0.9221×0.4) while the value of the filmthickness ratio Γ is maintained at 0.4. In this manner, the reflector 4described in this embodiment has the structure that the total thicknessof the Si layer 2 and Mo layer 3, i.e., a periodical length of therepetitive stack unit, is 6.95 nm. In this case, since Γ=0.4, a filmthickness of one Si layer 2 is 4.17 nm and a film thickness of one Molayer 3 is 2.78 nm.

The reflector 4 structured as above has a reflectance spectrum by asingle reflector wherein as shown in FIG. 5 the center of FWHM is notcoincident width the center wavelength of exposure light. However, forthe reflectance R via thirteen reflection surfaces in total, as shown inFIG. 6 the center of FWHM is coincident with the center wavelength ofexposure light. This may be ascribed to that since the periodical lengthof a film thickness of the repetitive stack unit of the multi-layer filmstructure, i.e., the optical periodical length, is different from aconventional length, the wavelengths strengthening through interferenceby the multi-layer film structure are also different so that the peakwavelength of the reflectance shifts.

Description will be made on a manufacture procedure for the reflector 4having this structure. FIG. 7 is a flow chart illustrating an example ofa reflector manufacture procedure. As illustrated in this drawing, whenthe reflector 4 is manufactured, first a reflectance spectrum isobtained at the route corresponding to the number of reflectors 4mounted on the exposure apparatus, particularly, thirteen reflectionsurfaces in total (Step 101, hereinafter Step is abbreviated to “S”).The reflectance spectrum may be actually measured by forming a sample ofthe reflector or may be obtained by utilizing simulation techniques.After the reflectance spectrum is obtained, it is judged whether thecenter of FWHM of the reflectance spectrum is coincident with the centerwavelength of exposure light of extreme ultraviolet light (S102). Ifthis judgement result indicates that both are not coincident, theperiodical length of a film thickness of the Si layer 2 and Mo layer 3of the multi-layer film structure is changed so as to make both becomecoincident (setting is performed again), and thereafter the reflectancespectrum is again obtained at the route of thirteen reflection surfacesin total (S101). These processes are repeated until both becomecoincident. It can be considered that the film thicknesses of the Silayer 2 and Mo layer 3 of the multi-layer film structure are set to havedesired values by properly adjusting the film forming speeds, forexample, of sputtering.

If the exposure apparatus, particularly an optical system formed byreflection mirrors, is structured by using the reflectors 4 formed inthe above-described manner (e.g., reflector having a periodical lengthof a film thickness of 6.95 nm and Γ of 0.4), the reflectance R becomescoincident with the center wavelength of exposure light even at theroute that extreme ultraviolet light propagates via thirteen reflectionsurfaces in total between the light source for extreme ultraviolet lightand the resist on a wafer. It is therefore possible to suppress a largeattenuation of the intensity of extreme ultraviolet light and retain asufficient energy for resist exposure.

Of the reflector 4 used by the exposure apparatus, a mask blankconstituting an exposure mask among others is frequently changed with acircuit pattern to be transferred. Therefore, an individual differenceis inevitable, namely, a film thickness variation of multi-layer filmstructures of mask blanks is inevitable. The film thickness variation ofmulti-layer film structures is mainly classified into two variations,variations of respective thicknesses d_(Si) of Si layers 2 andrespective thicknesses d_(Mo) of Mo layers 3 and a variation of totalfilm thicknesses d_(total) after 40 layers are stacked. This relation isrepresented by the following equation (2): $\begin{matrix}{d_{total} = {{\sum\limits_{j}^{40}\quad{djSi}} + {\sum\limits_{j}^{40}\quad{djMo}}}} & (2)\end{matrix}$wherein the variations of respective thicknesses d_(Si) of Si layers 2and respective thicknesses d_(Mo) of Mo layers 3 do not influencegreatly the intensity reduction by reflection of extreme ultravioletlight if the variation of total film thicknesses d_(total) is restrictedin a desired range. This can be confirmed by calculating the reflectanceR_(total), for example, via the route of thirteen reflection surfaces ofthe exposure apparatus including twelve reflection mirrors structured tohave a periodical length of a film thickness of 6.95 nm and Γ=0.4 andone mask blank having a film thickness variation, by using the followingequation (3) and a reflectance R₁₂ via twelve reflection mirrors and areflectance R_(mask) of the mask blank having a film thicknessvariation.R _(total) =R ₁₂ ×R _(mask)  (3)

More specifically, the mask blanks having variations of d_(Si) andd_(Mo) are used, and the energies reaching resist on a wafer at standarddeviations 3σ=0.5 nm and 3σ=1.0 nm are compared with the energy at3σ=0.0 nm. More in detail, the energy E_((3σ=0.5))=∫R_(total) dλ at3σ=0.5 nm and the energy E_((3σ=1.0))=∫R_(total) dλ at 3σ=1.0 nm areobtained, and these energies are compared with the energyE_((3σ=0))=∫R_(total) dλ at 3σ=0.0 nm. These comparisons are performedby using the following equations (4) and (5):E _(relative) =E _((3σ=0.5)) /E _((3σ=0))  (4)E _(relative) =E _((3σ=1.0)) /E _((3σ=0))  (5)

The comparison results of reaching energies at three types of variations(variations A to C) obtained by using the equations (4) and (5) areshown in FIG. 8. In this case, if E_(relative)≧0.95 is used as thejudgement criterion based on the rule of thumb, as apparent from theexample shown in the drawing, the energy reaching degree does not poseany problem at 3σ=0.5 nm, and any problem occurs even at 3σ=1.0 nm forthe two types of variations (variations A and B). With respect to theseresults, in the actual mask blank manufacture process, it is possible tocontrol the variation width narrower than that at 3σ=0.5. If theseresults are considered synthetically, it can be said that thesevariations do not pose any problem even if there are variations of thefilm thickness d_(Si) of Si layer 2 and the film thicknesses d_(Mo) ofMo layers 3.

As different from the variations of the film thicknesses d_(Si) andd_(Mo) of the layers, the variation of the total film thicknessesd_(total) greatly influences the intensity reduction of extremeultraviolet light by reflection. This can be ascribed to that, forexample, in the case of a multi-layer film structure having Γ=0.4, evenif the center of FWHM of the reflectance spectrum is made coincidentwith the center wavelength of exposure light of extreme ultravioletlight as described previously, the center of FWHM shifts to the shorterwavelength side from the center wavelength of exposure light if thetotal film thicknesses d_(total) of the multi-layer film structure havea variation and become thinner than a desired value, whereas the centerof FWHM shifts to the longer wavelength side from the center wavelengthof exposure light if the total film thickness becomes thicker than thedesired value. FIG. 9 shows reflectances R_(mask) at variations from −3nm to +3 nm of the total film thicknesses d_(total) of multi-layer filmstructures wherein, for example, Γ is 0.4, the film thickness of the Silayer 2 is 4.17 nm, the film thickness of the Mo layer 3 is 2.78 nm andthe periodical length of the repetitive stack unit is 6.95 nm. It can beseen from the example shown in the drawing that the center of FWHM ofthe reflectance R_(mask) shifts to the shorter or longer wavelength sideof the center wavelength of exposure light in accordance with thevariation of the total film thicknesses d_(total).

As different from the variations of the film thicknesses d_(Si) andd_(Mo) of the layers, the variation of the total film thicknessesd_(total) is required that a variation width thereof is restricted in apredetermined constant allowable range.

A variation width of the total film thickness d_(total) can be obtainedas in the following for multi-layer film structures having, for example,Γ of 0.4. First, basing upon the results shown in FIG. 9, thereflectances R_(total) via thirteen surfaces in total relative to thevariations of the total film thicknesses d_(total) are obtained. Theresults are shown in FIG. 10. The energies reaching resist on a waferare obtained from the results shown in FIG. 10 and compared each other.More specifically, for example, the total film thickness d_(total) ischanged from −3 nm to +3 nm and the reaching energiesE(Δd_(total)=−3)=∫R_(total) dλ, E(Δd_(total)=−2)=∫R_(total) dλ,E(Δd_(total)=−1)=∫R_(total) dλ, E(Δd_(total)=+1)=∫R_(total) dλ,E(Δd_(total)=+2)=∫R_(total) dλ, E(Δd_(total)=+3)=∫R_(total) dλ areobtained and compared with the reaching energyE(Δd_(total)=0)=∫R_(total) dλ with no variation.

Namely, the relative energies reaching the wafer at the variations ofthe d_(total) are obtained, includingE_(relative)=E(Δd_(total)=−3)/E(Δd_(total)=0),E_(relative)=E(Δd_(total)=−2)/E(Δd_(total)=0),E(Δd_(total)=−1)/E(Δd_(total)=0),E_(relative)=E(Δd_(total)=0)/E(Δd_(total)=0),E_(relative)=E(Δd_(total)=+1)/E(Δd_(total)=0),E_(relative)=E(Δd_(total)=+2)/E(Δd_(total)=0), andE(Δd_(total)=+3)/E(Δd_(total)=0). The comparison results of the energiesE_(relative) obtained in this manner are shown in FIG. 11.

The allowable range of the variation of d_(total) can be obtained fromthe comparison results of the energies E_(relative) relative toΔd_(total). Namely, if E_(relative)≧0.95 based on the rule of thumb isused as the judgement criterion, it can be seen also from the resultsshown in FIG. 11 that the allowable variation of d_(total) is in therange from −2.195 nm to +2.755 nm and in the range width of 4.95 nm. Inother words, for multi-layer film structures having Γ of 0.4, avariation of 1.78% is allowable for the reference value d_(total)=278nm.

However, if the productivity of, for example, a mask blank, isconsidered, it is needless to say that the allowable variation ofd_(total) is desired to have a broad width. In this context, multi-layerfilm structures are not configured to make the variation of the totalfilm thicknesses d_(total) falls in the allowable range while Γ is fixedto a constant value, but the allowable range of the variation ofd_(total) can be broadened by selecting an optimum Γ value together withthe above-described periodical length of the film thickness of themulti-layer film structure.

Detailed description will be made on selecting an optimum Γ value. Forexample, the relation between the periodical length of the filmthickness and an optimum Γ of a multi-layer film structure is given, forexample, as shown in FIG. 12. More specifically, if the periodicallength of a film thickness is 6.88 nm, Γ=0.25 (in this case, the totalfilm thickness d_(total)=275.2 nm, the film thickness of one Silayer=5.1600 nm and the film thickness of one Mo layer=1.7200 nm); ifthe periodical length of a film thickness is 6.90 nm, Γ=0.30 (in thiscase, the total film thickness d_(total)=276.0 nm, the film thickness ofone Si layer=4.8300 and the film thickness of one Mo layer=2.0700 nm),Γ=0.25 (in this case, the total film thickness d_(total)=275.2 nm, thefilm thickness of one Si layer=5.1600 nm and the film thickness of oneMo layer=1.7200 nm); if the periodical length of a film thickness is6.90 nm, Γ=0.30 (in this case, the total film thickness d_(total)=276.0nm, the film thickness of one Si layer=4.8300 nm and the film thicknessof one Mo layer=2.0700 nm); if the periodical length of a film thicknessis 6.92 nm; Γ=0.35 (in this case, the total film thicknessd_(total)=276.8 nm, the film thickness of one Si layer=4.4980 nm and thefilm thickness of one Mo layer=2.4220 nm); if the periodical length of afilm thickness is 6.95 nm, Γ=0.40 (in this case, the total filmthickness d_(total)=278.0 nm, the film thickness of one Si layer=4.1700nm and the film thickness of one Mo layer=2.7800 nm); if the periodicallength of a film thickness is 6.98 nm, Γ=0.45 (in this case, the totalfilm thickness d_(total)=279.2 nm, the film thickness of one Silayer=3.8390 nm and the film thickness of one Mo layer=3.1410 nm); ifthe periodical length of a film thickness is 7.01 nm, Γ=0.50 (in thiscase, the total film thickness d_(total)=280.4 nm, the film thickness ofone Si layer=3.5050 nm and the film thickness of one Mo layer=3.5050nm); if the periodical length of a film thickness is 7.03 nm, Γ=0.55 (inthis case, the total film thickness d_(total)=281.2 nm, the filmthickness of one Si layer=3.1635 nm and the film thickness of one Molayer=3.8665 nm); and if the periodical length of a film thickness is7.05 nm, Γ=0.60 (in this case, the total film thickness d_(total)=282.0nm, the film thickness of one Si layer=2.8200 nm and the film thicknessof one Mo layer=4.2300 nm).

FIG. 13 shows reflectances by a single multi-layer film structure, i.e.,by a single reflection surface when optimum Γ values are selected. Itcan be understood from the example shown in the drawing that even if thetotal thickness d_(total) shifts, the wavelength giving the peakintensity will not be changed by optimizing a combination of theperiodical length of a film thickness and Γ value.

FIG. 14 shows reflectances R_(total) via thirteen surfaces in total whenoptimum Γ values are selected. It can be understood from the exampleshown in the drawing that the half value center of the reflectance isalways coincident with the center wavelength of exposure light at 13.5nm.

The energies reaching resist on a wafer are obtained from the resultsshown in FIG. 14 and they are compared each other. Specifically, thereaching energies when the optimum Γ values are selected are obtained,including E(Γ=0.25)=∫R_(total) dλ, E(Γ=0.30)=∫R_(total) dλ,E(Γ=0.35)=∫R_(total) dλ, E(Γ=0.40)=∫R_(total) dλ, E(Γ=0.45)=∫R_(total)dλ, E(Γ=0.50)=∫R_(total) dλ, E(Γ=0.55)=∫R_(total) dλ, andE(Γ=0.60)=∫R_(total) dλ, and compared with E(Γ=0.40)=∫R_(total) dλ usedas a reference.

Namely, the relative energies reaching the wafer at the variations ofd_(total) are obtained, including E_(relative)=E(Γ=0.25)/E(Γ=0.40),E(Γ=0.30)/E(Γ=0.40), E(Γ=0.35)/E(Γ=0.40), E(Γ=0.40)/E(Γ=0.40),E(Γ=0.45)/E(Γ=0.40), E(Γ=0.50)/E(Γ=0.40), E(Γ=0.55)/E(Γ=0.40), andE(Γ=0.60)/E(Γ=0.40). The comparison results of E_(relative) obtained inthis manner are shown in FIG. 15.

The allowable range of the variation of d_(total) can be obtained fromthe comparison results of E_(relative) obtained in this manner. Namely,if E_(relative)≧0.95 based on the rule of thumb is used as the judgementcriterion, it can be seen also from the results shown in FIG. 15 thatthe allowable variation of d_(total) is in the range from −2.220 nm to+3.585 nm and in the range width of 5.805 nm. This means that avariation of 2.09% is allowable for the reference value d_(total)=278nm.

Namely, if the multi-layer film structure is configured not by fixing Γto a constant value but by selecting an optimum Γ value together withthe periodical length of a film thickness, the allowable variation valueof the total thickness d_(total) of the multi-layer film structureincreases. FIG. 16 shows the results obtained by plotting the allowablevariation values of the total film thickness d_(total) as a function ofE_(relative) in both cases when the Γ value is optimized and notoptimized. It can be seen also from the example shown in the drawingthat if the Γ value is optimized, the allowable variation valueincreases more than if the Γ value is not optimized, and that in thesame variation range, a lager energy can be obtained than if the Γ valueis not optimized.

It can be considered from this that of the reflectors 4 used by theexposure apparatus, the mask blank constituting the exposure mask amongothers is manufactured by selecting the optimum Γ value together withthe periodical length of a film thickness. Namely, in the mask blankmanufacture process, if d_(total) is shifted from the d_(total)reference value of 278 nm at Γ=0.40, the film forming conditions areselected from FIG. 12 so as to obtain an optimum relation between the Γvalue and d_(total).

More specifically, as shown in FIG. 7, after the exposure apparatus isconfigured having twelve reflection surfaces of the reflection mirrorshaving the periodical length of a film thickness set in the manneralready described (S103), a mask blank used for the exposure apparatusis manufactured (S104). Before this manufacture, first the total filmthickness d_(total) of the multi-layer film structure is obtained(S105). The total film thickness d_(total) may be actually measured byforming a sample of the mask blank or may be obtained by utilizingsimulation techniques. It is assumed that the multi-layer film structurehas Γ of 0.40.

After the total film thickness d_(total) is obtained, the periodicallength of the film thickness at the total film thickness d_(total) isobtained (S106) to judge whether the periodical length of the filmthickness is shifted from a predetermined reference value, e.g., thereference value of 278 nm at Γ=0.40. If it is shifted from the referencevalue, the Γ value is optimized to change the periodical length of thefilm thickness and Γ value (to perform setting again) and thereafter theabove-described Steps are repeated.

Namely, in manufacturing a mask blank, in addition to the periodicallength of the repetitive stack unit of the multi-layer film structure,the Γ value, which is the film thickness ratio between the Si layer andMo layer constituting the repetitive stack unit, is also set in such amanner that the center of FWHM of the reflectance R_(total) via thirteensurfaces in total becomes coincident with the center wavelength ofextreme ultraviolet light (refer to FIG. 14) to configure themulti-layer film structure.

As the exposure mask is constituted of the mask blank obtained in thismanner, the allowable variation width of the total film thicknessd_(total) can be broadened. It can therefore be expected that theproductivity of mask blanks (exposure masks) is improved so that it ispossible to realize the improvement on a manufacture efficiency ofsemiconductor devices, the reduction of a manufacture cost and the like.Furthermore, also in this case, since it is possible to suppress theintensity of extreme ultraviolet light from being attenuatedconsiderably, a sufficient reaching energy for exposure to resist can beretained and it is possible to avoid beforehand the manufacture qualityand the like of semiconductor devices from being degraded.

In this description, although optimization of the Γ value is used by wayof example when a mask blank is manufactured, it is obvious that the Γvalue is optimized when a reflection mirror is manufactured. Namely, theoptimization of the Γ value described in the embodiment is applicable toall types of reflectors for extreme ultraviolet light. Therefore,remarkable effects can be obtained relative to the film thicknessvariation of, for example, a half tone phase shift mask blank, byoptimizing the Γ value.

Description will be made on application of the optimization of a Γ valueof a half tone phase shift mask blank. As an example of a half tonephase shift, a mask blank of a multi-layer film structure for reflectingextreme ultraviolet light is used on which a TaN film of extremeultraviolet light absorbing material is formed with a Ru film beinginterposed therebetween. This half tone phase shift mask provides aphase shift mask function by setting a phase difference of 180 degreesbetween light reflected from the reflection surface of the mask blankand light reflected from the surface of the TaN film. For example, thefilm thicknesses giving a phase difference of 180 degrees are 13 nm forthe R film and 30 nm for the TaN film.

FIGS. 17 and 18 show the wavelength dependency of a phase differencewhen the Γ value is not optimized relative to the variation of the totalfilm thicknesses d_(total) of mask blanks of the above-described halftone phase shift mask. FIG. 17 is a diagram showing the phase differencedistribution of TE waves, and FIG. 18 is a diagram showing the phasedifference distribution of TM waves. It can be seen from the examplesshown in these drawings that the phase difference range is from 167degrees to 184 degrees if the Γ value is not optimized.

In contrast, FIGS. 19 and 20 show the wavelength dependency of a phasedifference when the Γ value is optimized relative to the variation ofthe total film thicknesses d_(total) of mask blanks of the half tonephase shift mask. FIG. 19 is a diagram showing the phase differencedistribution of TE waves, and FIG. 20 is a diagram showing the phasedifference distribution of TM waves. It can be seen from the examplesshown in these drawings that the phase difference distribution width isimproved from 167 degrees to 183 degrees if the Γ value is optimized.Namely, by optimizing the Γ value, the phase difference distributionwidth is improved by about 6%.

FIG. 21 shows a ratio T_(ratio)=T_((Ru+TaN))/T_(blank) of a reflectanceT_((R+TaN)) of the R film and TaN film when the Γ value is not optimizedrelative to the variation of the total film thicknesses d_(total) ofmask blanks to a reflectance T_(blank) of mask blanks. This ratioT_(ratio) is desired to have a small distribution, similar to the phasedifference distribution. In contrast, FIG. 22 shows the ratio T_(ratio)when the Γ value is optimized. From the comparison of these examplesshown in the drawings, it can be seen that the wavelength dependency ofthe reflectance ratio becomes small by optimizing the Γ value.

Namely, as the optimization of the Γ value is applied to the blank ofthe half tone phase shift mask, a phase shift mask can be realizedwherein not only the variation width of the total film thicknessd_(total) is broadened, but also the phase difference distribution andreflectance ratio distribution are small.

In the above description, although the exposure apparatus constituted ofthirteen reflection surfaces in total is used by way of example, theinvention is also applicable to exposure of different types. FIG. 23 isa diagram showing an example of the outline structure of anotherexposure apparatus. In an exposure apparatus 10 in the example shown inthe drawing, exposure light output from a light source 11 of extremeultraviolet light is separated by a beam splitter 12, narrowed to aproper angle by a prism unit 13 and passes through a fly eye lens 14 toform modified illumination or annular illumination to be describedlater. This light is reflected by (or transmitted through) a maskpattern of a reticle 16 via an illumination lens system 15, converged bya focussing lens system 17, and becomes obliquely incident illuminationfor resist coated on a wafer 18. Instead of using the beam splitter 12and prism unit 13, the modified illumination or half tone annularillumination may be formed by using a filter which transmits an amountof light equal to or larger than some degree through a light sourcecenter and its nearby area. Further, if a mercury lamp is used as thelight source 3 shown in FIG. 2, an exposure apparatus with an i-linestepper can be realized. The invention is not limited to this, but othertypes of exposure apparatuses may also be used such as a g-line stepper,a KrF excimer laser stepper and an ArF excimer laser stepper.

The exposure beam is not limited only to extreme ultraviolet light butother beams may be used such as ultraviolet light, an electron beam, anX-ray, a radial ray, a charged particle ray and a light ray, with whichthe present invention can be properly reduced in practice.

For example, one of electron beam exposure techniques is low energyelectron proximity projection lithography (LEEPL). LEEPL uses a stencilmask made of a membrane having a thickness of several hundreds nm andformed with holes corresponding to a device pattern. A mask is disposedjust above a wafer at a distance of several tens, m between the mask andwafer. The pattern area of the mask is scanned with an electron beam atseveral tens keV to transfer the pattern to the wafer (T. Utsumi,Journal of Vacuum Science and Technology B17, 2897 (1999)). In thismanner, an electron beam emitted from a low acceleration electron gunpasses through an aperture, is changed to a parallel beam by a condenserlens, and passes through a deflector to be irradiated on a wafer via themask. Also in this case, by using a mask described in the presentinvention, it becomes possible to properly deal with a micro finepattern width and pattern pitch of a transfer image so that the presentinvention can contribute to the improvement on the performance ofsemiconductor devices.

There is a method of supporting a small segment membrane by a beamstructure (grid structure). This is used by a mask of SCALPEL(scattering with angular limitation in projection electron-beamlithography), PREVAIL (projection exposure with variable axis immersionlenses) and an EB stepper (for example, L. R. Harriott, Journal ofVacuum Science nd Technology B15, 2130 (1997); H. C. Pfeiffer, JapaneseJournal of Applied Physics 34, 6658 (1995)). With SCALPEL, an electronbeam emitted from a low acceleration electron gun passed through anaperture, is changed to a parallel beam by a condenser lens, and passesthrough a deflector to be irradiated to a wafer via a mask. WithPREVAIL, a condenser lens, a reticle, a first projection lens, acrossover aperture, a second projection lens, a sample, a lens under thesample are sequentially arranged from an electron source side totransfer a reticle pattern to the sample. Also in these cases, by usinga mask described in the present invention, it becomes possible toproperly deal with a micro fine pattern width and pattern pitch of atransfer image so that the present invention can contribute to theimprovement on the performance of semiconductor devices.

Even if not only extreme ultraviolet light, but also ultraviolet light,an electron beam, an X-ray, a radial ray, a charged particle ray or alight ray is used as the exposure beam, a line width variation and apattern position misalignment after exposure to a wafer can be minimizedby applying the present invention. Therefore, it becomes possible toproperly deal with a micro fine pattern width and pattern pitch of atransfer image so that the present invention can contribute to theimprovement on the performance of semiconductor devices.

Industrial Applicability

As described above, according to a reflector for extreme ultravioletlight, its manufacture method, a phase shift mask, an exposure apparatusand a semiconductor manufacture method of the present invention, thewavelength dependency of a reflectance via a plurality of reflectionsurfaces can be made coincident with the center wavelength of exposurelight of extreme ultraviolet light. Accordingly, it is possible toretain a sufficient reaching energy for exposure of a subject to beexposed. Further, if an optimum r value is selected, the allowablevariation width of a film thickness of the reflector can be broadened sothat a sufficient energy reaching an exposure subject can be retainedwithout degrading the productivity and the like of reflectors.

1. A reflector for exposure light, characterized in that: said reflectorfor exposure light has a multi-layer film structure that a plurality oflayers are repetitively stacked in the same order; a periodical lengthof a repetitive stack unit of said multi-layer film structure is set sothat a center of full width at half maximum of a reflectance via apredetermined number of reflectors becomes coincident with a centerwavelength of said exposure light to be reflected, and said reflectorfor exposure light is used when said exposure light is exposed to asubject to be exposed in a lithography process for manufacture of asemiconductor device.
 2. A reflector for exposure light according toclaim 1; characterized in that: in addition to said periodical length ofsaid repetitive stack unit of said multi-layer film structure, a filmthickness ratio between a plurality of layers constituting saidrepetitive stack unit is set so that said center of full width at halfmaximum of said reflectance via said predetermined number of reflectorsbecomes coincident with said center wavelength of exposure light to bereflected.
 3. A reflector for exposure light according to claim 1;wherein said exposure light is any one of extreme ultraviolet light,ultraviolet light, an electron beam, an X-ray, a charged particle ray, aradial ray, or a visible light.
 4. A reflector for exposure lightaccording to claim 1; wherein said multi-layer film structure is made bystacking constituted of Si and Mo in the same order.
 5. A reflector forexposure light according to claim 4; wherein said multi-layer filmstructure is stacked on a glass substrate comprising SiO₂ from saidglass surface toward the surface of said reflector.
 6. A method ofmanufacturing a reflector for exposure light, characterized in that; amulti-layer film structure made by repetitively stacking a plurality oflayers in the same order is formed by setting a periodical length of arepetitive stack unit of said multi-layer film structure and a filmthickness ratio between a plurality of layers constituting saidrepetitive stack unit in such a manner that a center of full width athalf maximum of a reflectance via a predetermined number of reflectorsbecomes coincident with a center wavelength of exposure light to bereflected.
 7. A method of manufacturing a reflector for exposure lightaccording to claim 6; wherein said exposure light is any one of extremeultraviolet light, ultraviolet light, an electron beam, an X-ray, acharged particle ray, a radial ray, or a visible light.
 8. A method ofmanufacturing a reflector for exposure light according to claim 6;wherein said multi-layer film structure is made by stacking constitutedof Si and Mo in the same order.
 9. A method of manufacturing a reflectorfor exposure light according to claim 8; wherein said multi-layer filmstructure is stacked on a glass substrate comprising SiO₂ from saidglass surface toward the surface of said reflector.
 10. A mask used whenexposure light is exposed to a subject to be exposed in a lithographyprocess for manufacture of a semiconductor device, said maskcharacterized by; including a reflector portion having a multi-layerfilm structure made by repetitively stacking a plurality of layers inthe same order and an absorption film portion covering the reflectorportion with a predetermined pattern; wherein said mask is structured sothat there is a phase difference between reflection light of exposurelight from said reflector portion and reflection light of said exposurelight from said absorption film portion, and that in said reflectionportion a periodical length of a repetitive stack unit of saidmulti-layer film structure and a film thickness ratio between theplurality of layers constituting said repetitive stack unit are set sothat a center of full width at half maximum of a reflectance via apredetermined number of reflectors becomes coincident with a centerwavelength of exposure light to be reflected.
 11. A mask according toclaim 10, wherein said mask is a phase shift mask.
 12. A mask accordingto claim 10; wherein said exposure light is any one of extremeultraviolet light, ultraviolet light, an electron beam, an X-ray, acharged particle ray, a radial ray, or a visible light.
 13. A maskaccording to claim 10; wherein said multi-layer film structure is madeby stacking constituted of Si and Mo in the same order.
 14. A maskaccording to claim 12; wherein said multi-layer film structure isstacked on a glass substrate comprising SiO₂ from said glass surfacetoward the surface of said reflector.
 15. A mask according to claim 10;wherein said buffer layer comprises Ru (ruthenium).
 16. A mask accordingto claim 15; wherein a light reflection surface side of said reflectoris covered with TaN (tantalum nitride)
 17. An exposure apparatus usedwhen exposure light is exposed to a subject to be exposed in alithography process for manufacture of a semiconductor device,characterized by: including a predetermined number of reflectors forexposure light, said reflector having a multi-layer film structure madeby repetitively stacking a plurality of layers in the same order;wherein in said reflector for exposure light a periodical length of arepetitive stack unit of said multi-layer film structure and a filmthickness ratio between the plurality of layers constituting saidrepetitive stack unit are set so that a center of full width at halfmaximum of a reflectance via said predetermined number of reflectorsbecomes coincident with a center wavelength of exposure light to bereflected.
 18. An exposure apparatus according to claim 17; wherein saidexposure light is any one of extreme ultraviolet light, ultravioletlight, an electron beam, an X-ray, a charged particle ray, a radial ray,or a visible light.
 19. A semiconductor device manufacture methodcharacterized by: including a reflector portion having a multi-layerfilm structure made by repetitively stacking a plurality of layers inthe same order and an absorption film portion covering the reflectorportion with a predetermined pattern; wherein exposure light is exposedto a subject to be exposed in a lithography process for manufacture of asemiconductor device; by using a mask structured so that there is aphase difference between reflection light of exposure light from saidreflector portion and reflection light of said exposure light from saidabsorption film portion, and that in said reflection portion aperiodical length of a repetitive stack unit of said multi-layer filmstructure and a film thickness ratio of said plurality of layersconstituting said repetitive stack unit are set so that a center of fullwidth at half maximum of a reflectance via a predetermined number ofreflectors becomes coincident with a center wavelength of exposure lightto be reflected.
 20. A semiconductor device manufacture method accordingto claim 19; wherein said exposure light is any one of extremeultraviolet light, ultraviolet light, an electron beam, an X-ray, acharged particle ray, a radial ray, or a visible light.